The present invention relates to apparatus and processes for the manufacture of integrated circuits, more specifically to those used for injecting and controlling the injection of chemicals during the processes of cleaning, rinsing, and/or drying of silicon wafers.
There has been a long felt need to improve the tank design for processing of wafers used in this industry. Current injection systems commonly utilize low dose diaphragm or bellow pumps to introduce chemicals into a pressurized deionized water pipe. The temperature of the mixture is either not controlled or relies on preheating or pre-cooling of the incoming deionized water for temperature adjustment. Concentration of the mixture is either not monitored or uses a Near Infra Red Spectrometer to measure the mixture""s concentration of each chemical injected with no feedback control.
There are several problems with these existing methods.
For example, low dose diaphragm pumps create discontinuity in the injection of chemicals due to the pulsing of the diaphragm, causing inaccuracies in the amount of chemical introduced into the mixture over time. Also, when chemicals with low vapor pressure are injected with low dose diaphragm pumps, bubbles can be produced during the suction stroke that can lock up the pump or cause inaccuracies in the dosing when these bubbles get trapped along the chemical lines or the pump chamber. As the pump ages, small particulates can be produced by the flexing of the diaphragm or bellow in the pump during dosing.
Existing injection systems rely on preheated or pre-cooled deionized water for temperature control. These systems lack response when temperature control over a narrow temperature range is needed on the fly during the chemical injection. Large heaters or chillers are also needed to cope with the high flow of deionized water used in the prior methods and systems.
Near Infra Red spectrometers are expensive and in current designs they are not used to provide feedback adjustment to control the amount of chemicals injected in real time. Conductivity sensors are cheaper and are sometimes used but currently there is no method available that can differentiate the amount of chemicals injected if more than one type of chemical is used.
An objective of the present invention is to produce a very consistent solution of one or more chemicals at selected concentration(s), temperature, and flow rate, for treating silicon wafers in a process tank.
Another objective of the invention is to adjust the concentration, temperature, and/or flow rate on the fly while maintaining consistency.
A further object is to provide a system which avoids the problems associated with Near Infra Red spectrometers in systems used to supply chemical solutions to silicon wafer process tanks.
These objects, and others which will become apparent from the following disclosure and the drawings, are achieved by the present invention which comprises, in one aspect, a system for use in treating of silicon wafers with chemicals during the manufacture of integrated circuits comprising a process tank for cleaning, rinsing, and/or drying silicon wafers; a first chemical supply vessel suitable for being pressurized, fluidly coupled to the process tank; a chemical flow sensor for electronically monitoring the flow rate of chemical from the first chemical supply vessel; a first chemical flow metering valve for electronically controlling the flow rate of chemical from the first chemical supply vessel; a supply of hot DI water fluidly coupled to the process tank; a hot water metering valve for electronically controlling the flow rate of hot DI water from the supply of the hot DI water; a supply of cold DI water fluidly coupled to the process tank; a cold water metering valve for electronically controlling the flow rate of cold DI water from the supply of cold DI water; a water flow sensor for electronically monitoring the flow rate of DI water; a system for mixing the DI water and the first chemical to produce a solution of the first chemical in water; a conductivity sensor to electronically measure the conductivity of solution of the first chemical in water; a temperature sensor to electronically measure the temperature of the solution being supplied to the process tank; and a control system for automatically adjusting the precise flow rate, temperature, and chemical concentration of solution supplied to the process tank.
In another aspect, the invention comprises method of injecting a solution of one or more chemicals in DI water into a process tank for cleaning, rinsing, and/or drying silicon wafers comprising pressurizing one or more chemical supply vessels fluidly coupled to the process tank; monitoring and controlling the flow rate of each chemical from each supply vessel; controlling the flow rate of hot DI water from a supply thereof; controlling the flow rate of cold DI water from a supply thereof, monitoring the flow rate of hot DI water from the supply thereof, cold DI water from the supply thereof, and/or a mixture of combined hot and cold DI water; mixing the hot and the cold DI water; mixing the first chemical with the mixture of the hot and the cold DI water and measuring the conductivity of the resultant solution of the first chemical in DI water; measuring the temperature of the solution of first chemical and any additional chemical(s) in DI water; and controlling the precise flow rate, temperature, and chemical concentration of the first and any additional chemicals in the solution supplied to the process tank.
The system for mixing the DI water and chemicals is preferably a chemical injection valve and a static mixer.
The water flow sensor system is either a total water flow sensor which measures the combined hot and cold DI water before it is combined with the first chemical, or it is separate water flow sensors for the hot and cold DI water before they are combined with each other and subsequently combined with the first and then any additional chemical(s).
In the preferred system, there are two chemical supply vessels, one for the first chemical and one for a second chemical, with the chemical flow from each vessel monitored with a flow sensor and metered with a metering valve. In systems having three or more chemical supply vessels, the chemical flow from each one is monitored and controlled in the same manner.
Nitrogen, preferably ultra pure nitrogen, is supplied under pressure to each chemical supply vessel to pressurize the vessel(s). Chemical can be supplied to the chemical supply vessel(s) from source(s) of bulk chemical(s) in conventional manners using conventional apparatus.
The controller can be a conventional programmed processor, although the programming is specific to the system of the invention. By continuously comparing the temperature of the solution supplied to the process tank with the desired, selected temperature, the controller is programmed to cause the proportion or ration of flow rate of hot DI water to cold DI water to be adjusted to achieve the desired temperature. The concentrations of the first and any second or additional chemicals are continuously controlled by the controller by monitoring the concentration of the first chemical in the solution. In the preferred system where there are two chemicals in the solution, the concentration of the solution of the first chemical and the concentration of the combined first and second chemicals are both used to determine the concentration of the second chemical. The flow rates of the first and second chemicals and the hot and cold DI water are continuously adjusted by the controller in order to provide very accurate concentrations of chemicals at the precise desired temperature.
The chemical supply vessel(s) and sources of DI water are fluidly connected, ultimately to the process tank, preferably using conventional piping or tubes.